Visible-light-induced tandem ring opening/1,6-conjugate addition of cyclobutanols with -quinone methides under metal- and additive-free conditions

We report, for the first time, a visible-light-promoted tandem ring opening/1,6-conjugate addition of cyclobutanols with p -quinone methides. This transformation proceeded smoothly in the presence of an organic photocatalyst [Mes-Acr-Me] + BF 4 − , affording a series of δ,δ-diaryl ketones in moderate to excellent yields. Notably, this practical reaction occurs under metal- and additive-free conditions and exhibits broad substrate scope and good functional group tolerance. Moreover, DFT calculations showed that the substrate p -quinone methides as Brønsted bases were significant to this transformation, which could activate the transient radical cations to form the key alkoxy radical intermediates. A visible-light-mediated tandem ring opening/1,6-conjugate addition of cyclobutanols with p -quinone methides was developed. This protocol allowed the formation of δ,δ-diaryl ketones in the presence of a readily available organic photocatalyst.